1. Field of the Invention
The present invention relates to a machine tool having a rotary table.
2. Description of the Related Art
In general, it is necessary for machineries with motion to have a brake to stop the motion. This is also the case for a machine tool, and the machine tool provided with a rotary table has a brake to index the rotary table at an indexed position by servo motor and firmly hold the rotary table at the position. This brake generally has a brake disc to operate brake action by pressing or the like of the brake disc.
In the brake with this configuration, frictional wear of a brake disc is caused by disturbance torque by machining load at the brake holding and so on, as brake operation is repeated. The brake disc has a life time, because efficient brake operation becomes difficult as the frictional wear progresses.
As for the machinery with a brake, such techniques are disclosed as disclosed in the patent literatures below.
Japanese patent Laid-Open No. 2012-202484 discloses a technique of break configuration with a brake disc of a rotary table, using the brake disc for clamping and unclamping.
In a technique disclosed in Japanese Patent Laid-Open No. 2004-51266, a brake operation number of a hoisting machine is used as an actual operation number in an elevator as a machine by comparing a number of brake operation times of the hoisting machine with a pre-set value, and a maintenance check operator is acknowledged of exceeding the pre-set value when it is the case.
Japanese Patent Laid-Open No. 2002-303344 discloses a technique of, detecting a predetermined amount of abrasion of a brake parts lining having reached a pre-set value by counting a brake pedal stepping-in, and displaying the same on a screen, in a vehicle brake.
Japanese Patent Laid-Open No. 5-281097 discloses a brake pad lifetime estimation technique determining a number of times of break operation reaches a predetermined value based on vehicle speed, deceleration, and a brake operation number.
The technique in Japanese Patent Laid-Open No. 2012-202484 discloses a brake disc on a rotary table, but do not consider lifetime estimation of the brake disc.
The techniques disclosed in Japanese Patent Laid-Open No. 2004-51266 and No. 2002-303344 estimate a brake disc lifetime by counting brake operation, however divergence is likely to occur between the brake lifetime estimated only by counting brake operation and an actual brake lifetime, since strength of brake disc holding force in the brake operation varies.
The technique disclosed in Japanese Patent Laid-Open No. 5-281097 considers vehicle speed and deceleration in addition to number of times of brake operation, however it is likely to be difficult to estimate the brake lifetime with precision when the vehicle speed or deceleration varies widely, since only such a correction is performed that, lifetime data of a brake pad in the technique is decreased when brake operation at vehicle velocity equal to or more than predetermined value is performed for predetermined number of times, or when deceleration is equal to or more than a predetermined value.